Archive for April, 2014

The mineral system CaCO3 has three crystalline polymorphs, vaterite being the thermodynamically least-stable form. Vaterite does not appear geologically, is rare as a biomineral and single crystal vaterite is particularly rare. The micrometer-sized spicules of the ascidian Herdmania momus – also known as sea squirts – has been studied in detail, showing that the spicules are single crystals of vaterite. Schenk and colleagues, at the University of Leeds, explore the processes used by organisms to generate single crystals of vaterite.

Selected as Editors choice for literature highlights in science magazine, this communication explores the possibility that organisms use the confinement intrinsic to biomineralisation processes to generate single crystals of vaterite. CaCO3 was precipitated within the pores of track-etched membranes in the absence of additives. The membranes were purchased from different sources, Millipore and Sterlitech. Each membrane produced different results. Precipitation of CaCO3 with the Millipore membrane led to the formation of a high yield of intra-membrane particles exhibiting rod-like morphologies. Structural investigation confirmed that vaterite was the major polymorph. In contrast, the Sterlitech membranes yielded very little intra-membrane material under the same reaction conditions. The authors suggest that the differences in CaCO3 precipitation within the two different membranes must originate from variations in the environments offered by the different membrane pores. These results demonstrate that subtle changes in microenvironment can have significant effects of polymorph production. For example the selectively of vaterite over the more stable polymorph calcite, achieved in this research, is likely to derive from the contrasting nucleation environments provided within the pores.

Compounds that change their molecular and electronic structure upon application of light are ideal candidates for sensors, switches and optical data storage medial. These photochromic molecules are now being pursued for use in MOFs in the hope of affording photonic control over the physical properties of the crystalline host. Several instances of MOFs containing non-covalently attached photochromic molecule have been reported, but there is a lack of control over guest orientation and concentration. The use of photoactive linkers means that the photochromic groups are covalently attached to the framework leading to MOFs with well-defined stoichiometry. In this report, a new class of photoswitchable linkers, based on diarylethene photochromes is introduced.

This article has been highlighted as a news story ‘metal organic frameworks react to light’ by Nina Notman in Materials Today

To read more about the full synthesis and characterization, including crystal structure analysis of reaction intermediates, download the full article for free*

Graphene nanoribbons (GNRs) are ultra-thin strips of graphene which exhibit technologically relevant optical, electronic and magnetic properties. How well these properties can be defined, understood and exploited depends on how precisely these ‘GNRs’ can be prepared. Top-down approaches to realise these materials from, for example, graphite, graphene or carbon nanotubes have been developed over recent years. However, the resultant materials are typically non-uniform, being wide, (relatively speaking) with a large amount of disorder.

The synthesis itself centres around the 3 step preparation of a multi-aryl containing dibromo pyrimidine monomer which is polymerised via a Yamamoto coupling using a nickel catalyst. The desired graphene structure is delivered via a cyclodehydrogenation Scholl reaction using ferric chloride. The molecular control from this route yields a very well defined structure. The only disorder introduced is a symmetrical one due to alternate possible sites for the four constituent nitrogen atoms present in each unit cell.

The 4N-GNR materials were deposited on a variety of supports to enable microscopic and surface analytics such as AFM, STM, TEM, XPS, EDX and Raman spectroscopy. The materials were observed to take on a ‘nanobelt’ conformation on deposition from sonicated dispersions. Particularly striking is the improvement in the fine structure reported in the Raman spectra, compared with typical signals for less well defined carbon materials, confirming the structural quality of the 4N-GNRs produced.

This communication will doubtless prove important to the development of sustainable synthetic routes to well defined graphene nanoribbons, enabling further study of the fascinating properties of these exciting new materials.

Read this RSC Chemical Communication today – access is free* for a limited time only!

The University of Bath will host Spring 2014 Royal Society of Chemistry Carbohydrate Group Meeting from Wednesday 30 April – Thursday 1 May.

On Wednesday evening, the 2014 RSC Haworth Memorial Lecture will be delivered by David Crich, Schaap Professor of Organic Chemistry at Wayne State University, Detroit, USA.

The Meeting will also include the Inaugural Buchanan Award Lecture in honour of J Grant Buchanan, a former Visiting Professorial Fellow in the Department of Chemistry here at Bath, who died two years ago on 17 April 2012, at the age of 85. Grant was a great researcher and educator, and is remembered fondly for his infectious enthusiasm, collegiality and warm humanity.

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